Sheet metal shaping apparatus and method



March 19, 1968 T. D. REYNOLDS 3,373,585

SHEET METAL SHAPING APPARATUS AND METHOD Filed Sept. 21, 1964 2Sheets-Sheet l March 19, 1968 T. D. REYNOLDS 3,373,585

SHEET METAL SHAPING APPARATUS AND METHOD Filed Sept. 21, 1964 2SheetsSneet 2 3,373,585 SHEET METAL SHAPING APPARATUS AND METHOD ThomasD. Reynolds, Winston-Salem, N.C., assiguor to R. J. Reynolds TobaccoCompany, Winston-Salem, N.C., a corporation of New Jersey Filed Sept.21, 1964, Ser. No. 397,766 9 Claims. (Cl. 7257) ABSTRACT OF THEDISCLOSURE A process and apparatus for drawing a sheet metal blank, theprocess comprising positioning the blank across a die cavity, forcingthe blank into the cavity while holding the cavity surrounding portionsthereof against the die with sufiicient force to only partially restrainthe lateral movement of these portions of the blank into the cavity, andthereafter forcing the blank further into the cavity while holding thecavity-surrounding portions thereof with a force sutficient tosubstantially completely restrain the lateral movement of theseportions. The apparatus comprises a first member including a die havinga cavity and a second member including a blank holder and a punch. Theforward end of the punch is sized to fit partially into the die cavityand spring means extends between the punch and the blank holder. Meansis provided for applying a fluid pressure between the forward end of thepunch and the blank to force the partially deformed blank further intothe cavity.

This invention relates to a sheet metal shaping apparatus and method andmore particularly to an improved apparatus and method wherein a sheetmetal blank is forced into and assumes the shape of a die cavity.

Heretofore the drawing of sheet metal has been accomplished either by apunch and die arrangement or by means of an arrangement wherein theblank is driven into the die cavity under fluid pressure. The punch anddie method of drawing commonly results in the stretching or drawing ofthe sheet in such a manner that the drawn product not only becomesthinner and harder than the blank from which it was formed but thestretching or drawing tends to take place non-uniformly over thestructure. This varied amount of stretching in the drawn product tendsto become accentuated as the punch and dies deteriorate with wear. Inaddition, there are a limited number of shapes which can be producedwith the punch and die technique. The dies involved are expensive, andlubricating oils which are necessary to the process quite often have tobe removed at the end of the process.

Air forming is one means for avoiding some of these difiiculties;however, even in the air forming processes which have been practicedto-date, work hardening is often non-uniform and localized. In general,the air forming processes prior to this invention appear to have beenlimited to rather shallow draws, unless interstage annealing wasemployed in the process.

It is therefore one object of this invention to provide an economicaland improved process and apparatus for drawing sheet metal.

It is an additional object of this invention to provide an improvedprocess for drawing sheet metal wherein the drawn product will be moreuniform in its strength and appearance.

It is still a further object of this invention to provide a process forforming sheet material which will permit the product to be formed in oneoperation and will eliminate the necessity for intermediate annealingstages.

It is still another object of this invention to provide a process fordrawing sheet metal blanks which will provide a uniformly good productwithout danger of scratch- .ing or rupturing during forming, thusresulting in subcompanying drawings.

The process for forming sheet material in accordance with this inventionis a two-step forming process. After the sheet metal blank has beenpositioned across the die having a cavity of suitable shape, the initialforming step of the process takes place. In this initial forming stepthe blank is forced partially into the die cavity, while at the sametime the portions of the blank which surround the cavity are heldagainst the corresponding cavity-surrounding portions of the die with aforce which is sufficient only to partially restrain the lateralmovement of these blank portions into the die cavity during this initialforming step.

Thereafter the second forming step takes place which consists of furtherdeforming the blank by forcing it further into the cavity while at thesame time holding the surrounding cavity portions of the blank againstthe die with a force which is of higher magnitude than the first forceand is sufiicient to substantially completely restrain the lateralmovement of these blank portions into the cavity during this furtherdeforming step.

It will be noted that in the first step of the process the materialsurrounding the die cavity is permitted a limited movement into the diecavity, whereas during the second step the cavity-surrounding materialis substantially pre vented from further moving into the die.

The preferred apparatus for drawing the sheet metal blanks comprises apair of members which are adapted to accommodate the blank therebetween.One of the members includes a die having a cavity of the desired shape.The other member includes an apertured blank holder for engaging andholding the portions of the sheet metal blank against the portions ofthe die surrounding the die cavity. The second member further includes apunch which has a forward end adapted to enter and force the blankpartially into the die cavity. This punch is disposed within theaperture of the blank holder, and either the punch on the one hand orthe blank holder and die on the other hand is relatively movable from aretracted position in which the forward end of the punch is withdrawnfrom the die cavity and an extended position wherein the forward end ofthe punch is disposed forwardly of the blank holder and partially withinthe cavity of the die.

Spring means acting between the blank holder and punch resiliently urgethe punch toward its retracted position, and the punch may be movedrelative to the blank holder to its extended position against theresistance of this spring means. While the punch is being so moved toits extended position, relative to the blank holder, the peripheralportions of the blank will be held against the die by the blank holderacting under the influence of the spring means, and when the punch hasreached its fully extended position, portions of the punch Will firmlyengage portions of the blank holder so that additional pressure on thepunch will result in a corresponding increase of the pressure on theblank holder and a corresponding increased gripping of the peripheralportions of the blank. Thus the initial forming is done by the punchmoving into the die cavity while the edges of the blank are lightlyrestrained against lateral movement. Means is provided for completingthe draw by fluid pressure forcing the blank the remaining way into thedie, and during this finishing step the peripheral edges of the blankare firmly held against movement.

With reference to the drawings:

FIGURE 1 is a side elevation View of an apparatus constructed inaccordance with this invention;

FIGURE 2 is a sectional elevation view showing the blank positioned overthe die cavity and held in place by the blank holder under the influenceof the spring means preliminary to the initial forming step;

FIGURE 3 shows the position of the punch relative to the blank holderand the die after the initial forming operation has been completed;

FIGURE 4 shows the portions of the apparatus and the formed blank afterthe second and final forming operation has been completed;

FIGURE 5 is a sectional elevation view showmg a modified form ofapparatus with the blank positioned in preparation for the first formingoperation;

FIGURE 6 is a sectional elevation view of the apparatus of FIGURE 5showing the position of the blank after the first forming operation; and

FIGURE 7 is a sectional elevation view of the apparatus of FIGURE 5showing the formed blank after the second and final forming operation.

With further reference to the drawings and particularly to FIGURE 1, theapparatus 10 is adapted to draw a flat sheet metal blank 11 into ahollow shell or dish of desired size and shape. This apparatus includesa two-part forming assembly 12 and means such as a hydraulic press 14for applying a mechanical force to the parts of the assembly 12. Theillustrated press 14 includes a first platen 16, a second platen 18 andmeans such as a hydraulic cylinder 19 and piston 20 for moving platens16 and 18 relatively toward and away from each other.

Hydraulic pressure to the cylinder 19 is supplied. through lines 21 and22, and a suitable hydraulic pressure gauge 24 may be provided to informthe operator of the level of pressure or force being exerted by thepress upon the forming assembly 12.

The forming assembly 12 consists of two parts or members, and thedetails of one embodiment of this assembly are best illustrated inFIGURES 2 through 4. The first part of the forming assembly comprises adie having a cavity 32 of the desired configuration. Suitable air vents34 extend through the die and communicate with the cavity 32, andcircumjacent the cavity 32, the die 30 has a laterally extending surface36.

The second part of the forming assembly overlies the die 30 and includesan apertured and preferably annular blank holder or holding ring 38, thecentral aperture 38a of which is approximately the same size as theopening into the cavity 32 of the die. A punch 40 is disposed formovement relative to the blank holder within the aperture 38a of theblank holder between a retracted position, as illustrated in FIGURE 2,and an extended position, as illustrated in FIGURES 3 and 4.

It will be noted that when in its extended position, the forward end 40aof the punch protrudes downwardly from the bottom surface of the blankholder 38, and this protruding forward end thus extends partially intothe cavity 32 of the underlying die. As will be later described, thisextension of the forward end of the punch provides the deformation ofthe blank during the first part of the drawing operation.

Resilient means such as springs 42 and 44 extend between the blankholder 38 and a shouldered portion 4% of the punch 40, and thus thepunch and blank holder are urged to their relative positions illustratedin FIGURES 1 and 2 wherein the punch is considered to be retracted.Thus, as the punch 40 is moved relative to the blank holder from itsretracted position, as illustrated in FIG- 4 URE 2, to its extendedposition, as illustrated in FIG-- URES 3 and 4, the blank 11 will beheld against the surface 36 of the die only by the resilient downwardforce exerted by the springs 42 and 44.

The resilient strength of the springs 42 and 44 is such that thesesprings will exert a sufficient force on the blank holder to efiectivelybut only partially restrain the peripheral portions of the blank fromslipping laterally inwardly toward the die cavity 32 during the initialforming stage as the punch moves relative to the blank holder to itsextended position. The effect of this limited and controlled slippingduring the initial forming stage is to moderately work harden theportion of the vertical wall of the partially drawn shell.

Extending to and through the forward end 40a of the punch is a conduit46 for conveying fluid under pressure to the top surface of the blank.The fluid is preferably air and the pressure may be obtained by means ofa suitable compressor 48 such as schematically illustrated in FIGURE 1.The air pressure may be indicated by a suitable pressure gauge 49 on theconduit 46.

During the second stage of the drawing operation, air under pressure inconveyed through conduit 46 to the top surface of the partially formedblank, as illustrated in FIGURE 3, and this air pressure forces theshell the remainder of the way into the die cavity 32 to the positionillustrated in FIGURE 4.

During the initial forming stage of the draw, which with the apparatusof FIGURES 2 through 4 is a punch and die forming stage, the blankholder 38 is totally dependent for its holding power upon the resilientstrength of the springs 42 and 44. During the second forming stage ofthe draw, however, the holding power of the blank holder 38 is notdependent upon the springs, but rather is dependent upon the externalforce applied to the punch and die, as by the press 14, to force thepunch and die together. This force is sufficient to insure that theblank is held with sutficient firmness between the blank holder 38 andthe surface 36 of the die to substantially completly restrain furtherlateral movement of the peripheral portions of the blank into the cavityduring the second forming stage of the draw.

The second or final air forming operation results in a product which hasa more uniform thickness and hardness than products achieved withpreviously employed processes and apparatus.

In the operation of the apparatus of FIGURES 2 through 4, the blank 11is positioned beneath the punch and blank holder portion of the formingassembly 12 so that it overlies the die and completely covers the diecavity 32. The force is exerted by the press 14 on the parts of theassembly 12 to press these parts together and, upon the exertion of thisforce, the blank holder 38 will engage and hold those portions of theblank which surround the cavity 32 against the top surface 36 of theunderlying die. This force will be dependent upon the compressiveresilience of the springs 42 and 44 as the punch 40 moves downwardlyrelative to the blank holder 38 toward its extended position. During itsdownward movement relative I to the blank holder the punch forces theblank downwardly and partially into the cavity 32 of the die until theposition illustrated in FIGURE 3 is reached. At this point theshouldered portion 40b of punch 40 firmly engages the blank holder 38and further pressure exerted on the punch and die by the press 14results in an increased squeezing action on the peripheral portions ofthe blank between the blank holder 38 and the cavity-surrounding surface36 of the die. This pressure will be sufiicient to hold these portionsof the blank against further lateral movement into the cavity as theblank is deformed by the application of air pressure through the conduit46 to the top surface of the partially formed blank.

A forming apparatus of modified form is illustrated in FIGURES 5 through7. In this apparatus the operation is a two-stage air draw rather than afirst-stage punch and die operation and second stage air draw as was thecase in the previous embodiment. In the apparatus of FIG URES 5 through7 a die 50 is employed having a cavity 52 with communicating air vents54, this die being substantially identical in all respects to the die 30of the previously described embodiment. Instead of employing a punch andblank holder, however, the apparatus of FIG- URES 5 through 7 employs acover plate 56 which also serves as a blank holder. This cover plate hasa fluid conduit 58 leading to the forward face thereof. The cover plate56 never enters the cavity 52 of the die, but instead merely overliesthe die 50 and die cavity 52. An external force may be applied to thedie and cover plate by the press 14 illustrated in FIGURE 1.

In the operation of the apparatus of FIGURES 5 through 7, the blank 11is inserted between the die 50 and the cover plate 56, and the die andcover plate are forced together by the press 14 under a first forcewhich is sufficient to only partially restrain the lateral inwardmovement of the peripheral portions of the blank during the initialforming stage. With this apparatus the initial forming is done by airapplied under pressure through the conduit 58, and the initial holdingforce on the cover plate and die is exerted until the air forces theblank partially into the die cavity 52, as illustrated in FIGURE 6.Thereafter the pressure on the holding plate 56 and die 50 is increasedso that the peripheral portions of the partially formed blank will begripped between these members with sufficient force to substantiallycompletely resist any further lateral movement of the peripheralportions of the blank as the partially formed blank is forced by airpressure the remainder of the way into the die cavity 52 to the positionillustrated in FIGURE 7.

It may be seen that with each of the two illustrated forming assemblyembodiments the peripheral portions of the blank 11 are only partiallyrestrained from lateral movement toward the die cavity during theinitial forming stage of the draw, and during the second and final stageof the draw the pressure on these peripheral portions is increased sothat their lateral movement toward the die cavity is substantiallycompletely restrained.

The apparatus of FIGURES 2 through 4 has the advantage of not requiringthe application of two pressures in the squeezing of the punch and dietogether. The lower holding force on the peripheral portions of theblank during the initial forming stage is accomplished automatical ly bythe resilience of the springs 42 and 44.

The apparatus of FIGURES 5 through 7 has the advantage of not requiringa punch, a separate holding ring, or springs for accomplishing theinitial holding force. Nevertheless, the apparatus of FIGURES 5 through7 does require the application of force by the press in two stages.

During the first stage of operation with both types of apparatus, theinitial holding force on the peripheral portions of the blank may, forexample, be on the order of 100 pounds per square inch. In the case ofthe embodiment illustrated in FIGURES 2 through 4, this initial holdingforce is accomplished by the springs 42 and 44, whereas in the case ofthe apparatus of FIGURES 5 through 7 this holding force is accomplishedby the pressure of the lower platen 18 against the die 50. During thesecond stage of the drawing operation the holding force on theperipheral portions of the blank may be increased substantially toperhaps 200 pounds per square inch or to double that of the initiallyapplied pressure. The holding pressures will, of course, vary accordingto the properties of the material and the forming pressures employed.

For a thin aluminum sheet of 3 to 5 mils in thickness, the initial airforming with the apparatus of FIGURES 5 through 7 may be accomplishedunder a pressure of, for example, 45 pounds per square inch. The airpressure employed to form the blank in the second or final forming stepof the draw with each of the embodiments illustrated in the case of theaforementioned thin aluminum sheet may, for example, be on the order ofpounds per square inch. These pressures will, of course, vary accordingto the thinness and physical properties of the material being formed,and according to the size, shape and depth of the cavity into which thematerial is to be formed.

The vents 34 in the embodiment of FIGS. 1-4, and the vents 54 in theembodiment of FIGS. 5-7 are provided to permit the ready egress of airfrom the die cavity as the blank is formed downwardly into the cavity.However, it may be desirable to use these or similar vents to facilitatethe application of at least a partial vacuum to the die cavity below theblank 11, to assist the positive forming pressure applied throughconduits 46 and 58 to the top of the blank.

It may be seen with the foregoing invention deeper draws can beaccomplished without producing wrinkles in the sheet and these draws maybe done on equipment which is of simplified construction and in a mannerwhich is quite economical. The formed product will be more uniformlyhardened and have a more uniform thinness and appearance than productsproduced by previously employed processes and apparatuses. Thisinvention eliminates the need for special lubricants or expensiveintermediate annealing steps, and the product may be formed completelyin one operation.

Further modifications of this invention will be apparent to thoseskilled in the art and it is desired, therefore, that my invention belimited only by the showing of the prior art and the scope of theappended claims.

I claim:

1. A process for drawing a sheet metal blank which comprises positioningthe blank across a die having a cavity, initially deforming the blank byforcing it into the cavity while simultaneously holding thecavity-surrounding portions thereof against the die with a first forcesufiicient only to partially restrain the lateral movement of theseblank portions into the cavity during the initial deforming step, andthereafter further deforming the blank by forcing it farther into thecavity while holding the cavity-surrounding portions against the diewith a second force sufficient to substantially completely restrain thelateral movement of these blank portions into the cavity during saidfurther deforming step.

2. A process for drawing a sheet metal blank which comprises positioningthe blank across a die cavity, forcing the blank partially into the diecavity while the portions of the blank surrounding the die cavity aregripped to permit controlled slipping of these portions into the cavityas the blank is deformed, whereby the peripheral portions of the blankwithin the cavity may be work hardened, and thereafter forcing the blankfarther into the cavity while the portions of the sheet surrounding thecavity are gripped tightly to prevent movement of these portions intothe cavity, whereby the remaining portions of the blank within thecavity may be work hardened.

3. A process for drawing a sheet metal blank which comprises positioningthe blank across a die having a cavity, initially deforming the blank byforcing it partially into the cavity while simultaneously holding thecavitysurrounding portions thereof against the die with a first forcesufficient only to partially restrain the lateral movement of theseblank portions into the cavity during the initial deforming step, andthereafter further deforming the blank by applying fluid pressure to thetop surface thereof sufficient to force it farther into the cavity whileat the same time holding the cavity-surrounding portions of the blankagainst the die with a second force sufficient to substantiallycompletely restrain the lateral movement of these blank portions intothe cavity during said further deforming step.

4. A process for drawing a sheet metal blank which comprises positioningthe sheet metal blank across a die having a cavity, initially deformingthe blank by causing fluid pressure between the bottom of the die cavityand the blank to be less than the fluid pressure on the opposite side ofthe blank, while simultaneously holding the cavity-surrounding portionsof the blank with a first force sufiicient only to partially restrainthe lateral movement of these portions into the cavity during theinitial deforming step, and thereafter further deforming the blank byincreasing the differential in fluid pressure on the opposite sides ofsaid blank to force the blank farther into the cavity whilesimultaneously holding the cavity-surrounding portions of the blank witha second force sufficient to substantially completely restrain thelateral movement of these blank portions into the cavity during saidfurther deforming step.

5. The process recited in claim 4 wherein the cavitysurrounding portionsof the blank are held against the corresponding portions of the die, andthe force exerted upon these portions during the initial deforming stepis substantially less than that exerted upon these portions during saidfurther deforming step.

6. The process according to claim 5, wherein the holding force on thecavity-surrounding portions of the blank during the initial deformingstep is on the order of about one half that of the force exerted onthese portions during said further deforming step.

'7. An apparatus for drawing a sheet metal blank, said apparatuscomprising a pair of members adapted to accommodate the blanktherebetween, one of said members including a die having a cavity, theother of said members including a blank holder for engaging and holdingportions of the blank against portions of the die circumjacent saidcavity, a punch having a forward end sized to fit partially into saiddie cavity, said punch being disposed for movement relative to saidblank holder between a retracted position in which said forward end iswithdrawn from said die cavity and an extended position in whichportions of said punch firmly engage said blank holder and the forwardend of said punch is extended from said blank holder and only partiallyinto said die cavity, spring means extending between said punch and saidblank holder and effective to urge said punch toward its retractedposition, whereby as said punch is moved to its extended position theblank will be partially forced into said cavity while said blank holderengages and holds the peripheral portions of the blank against the diecircumjaceut the cavity only under the influence of said spring meansand means for forcing the blank farther into said die cavity after saidpunch has firmly engaged the blank holder to substantially increase theholding force against the peripheral portions of the blank.

8. An apparatus for drawing a sheet metal blank, said apparatuscomprising a pair of members adapted to accommodate the sheet metalblank there-between, one of said members including a die having a ventedcavity, and the other of said members including an apertured blankholder for engaging and holding portions of the blank against portionsof the die surrounding said cavity, a punch having a forward end sizedto fit into said die cavity and conduit means for conducting fluid underpressure to said forward end, said punch being disposed for movementwithin the aperture of said blank holder between a retracted position inwhich said forward end is withdrawn from said die cavity and an extendedposition in which portions of said punch firmly engage said blank holderand the forward end of said punch is extended from said blank holder andpartially into said die cavity, and spring means extending between saidblank holder and said punch and urging said punch to its retractedposition, whereby as said punch is moved to its extended position theblank will be partially forced into said cavity while said blank holderengages and holds the peripheral portion of the blank against the diecircumjacent the cavity only under the influence of said spring means.

9. An apparatus for drawing a sheet metal blank, said apparatuscomprising a pair of members adapted to accommodate the sheet metalblank therebetween, one of said members including a die having a ventedcavity, and the other of said members including an apertured blankholder for engaging and holding portions of the blank against portionsof the die surrounding said cavity, a punch having a forward end size tofit into said die cavity and conduit means for conducting fluid underpressure to said forward end, said punch being disposed for movementwithin the aperture of said blank holder between a retracted position inwhich said forward end is withdrawn from said die cavity and an extendedposition in which portion of said punch firmly engage said blank holderand the forward end of said punch is extended from said blank holder andpartially into said die cavity, and spring means extending between saidblank holder and said punch and urging said punch to its retractedposition, whereby as said punch is moved to its extended position theblank will be partially forced into said cavity while said blank holderengages and holds the peripheral portion of the blank against the diecircumjacent the cavity only under the influence of said spring means,and power means for exerting a force on said punch greater than thatrequired to move it to its extended position, whereby after the partialforming of said blank by said punch the holding force on the peripheralportions of the blank may be increased preparatory to forcing said blankfarther into the cavity under fluid pressure.

References Cited UNITED STATES PATENTS 562,309 6/ 1896 Leavenworth 7260873,297 12/ 1907 Chillingworth 72--348 1,270,933 7/1918 Elsener 113-1201,711,445 4/ 1929 Burvenick 113-120 1,837,720 12/1931 Lucf et al.72--348 FOREIGN PATENTS 915,327 7/ 1954 Germany.

RICHARD J. HERBST, Primary Examiner.

